class Solution {
    int dx[4] = {0, 0, -1, 1};
    int dy[4] = {1, -1, 0, 0};
    int m = 0, n = 0;
 
public:
    void solve(vector<vector<char>>& board) {
        m = board.size(), n = board[0].size();
        for(int i = 0; i < n; ++i) // 修改边界的O成无关字符
        {
            if(board[0][i] == 'O')
                bfs(board, 0, i);
            if(board[m - 1][i] == 'O')
                bfs(board, m - 1, i);
        }
        for(int i = 0; i < m; ++i)
        {
            if(board[i][0] == 'O')
                bfs(board, i, 0);
            if(board[i][n - 1] == 'O')
                bfs(board, i, n - 1);
        }
 
        for(int i = 0; i < m; ++i) // 把剩下的O全修改成X，R全修改成O
        {
            for(int j = 0; j < n; ++j)
            {
                if(board[i][j] == 'O')
                    board[i][j] = 'X';
                else if(board[i][j] == 'R')
                    board[i][j] = 'O';
            }
        }
    }
 
    void bfs(vector<vector<char>>& board, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({i, j});
        board[i][j] = 'R';
        while(!q.empty())
        {
            auto [a, b] = q.front();
            q.pop();
            for(int i = 0; i < 4;  ++i)
            {
                int x = a + dx[i], y = b + dy[i];
                if(x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O')
                {
                    q.push({x, y});
                    board[x][y] = 'R';
                }
            }
        }
    }
};